Sorters of the general type here involved are shown, for example, in U.S. Pat. No. 5,393,042 granted Feb. 28, 1995, as well as in pending application, Ser. No. 334,907, filed Nov. 7, 1994 for Telescoping Registration For Sheet Receivers (now U.S. Pat. No. 5,531,437, Jul. 2, 1996) which is co-owned herewith and to which reference may be made for an understanding of the prior art.
Such sorters typically have a number of trays extending upwardly at an angle in the direction of sheet infeed from a horizontal plane, and the trays are progressively moved by appropriate cams upwardly and downwardly past the sheet entry location so as to receive sheets in collated or sorted relation or in groups or sets. Routinely the trays have had a length necessary to accommodate sheets of various sizes, say, ranging from normal letter size paper with a dimension of 81/2.times.11" to larger sheets of paper on the order of 11.times.17". The length of the trays heretofore has been of such dimension as to accommodate the longest sheet dimension for which the sorter is designed in such a way that the surface area of the tray is sufficient to fully support a smaller size sheet and the lengthwise dimension of the tray is sufficiently long as to avoid drooping of the outer ends of the larger size sheets.
Such construction of the trays has typically required the use of trays of such a length that the overall footprint of a sorting machine embodying the trays is fairly large as a function of the tray length.
Also, the per tray cost of such sorter is a function of the size of the trays due to the cost of tray material.
The same problems apply, also, in the case of fixed bin sorters of the type wherein sheets of paper are fed from a sheet transport system by appropriate gating mechanisms, as illustrated in U.S. Pat. No. 4,591,914 granted Sep. 8, 1987, for example.
In either case, sorters of the types shown in the prior art referred to above have trays which extend upwardly at an angle from the point of horizontal entry of sheets of paper into the tray, and the trays have been of such length, as a matter of necessity, either to fully support the maximum size of sheets to be received by the trays or, at least sufficiently long as to prevent excessive overhang of a sheet or a set of sheets beyond the outer end of the tray to the extent that the sheet or set of sheets droops or hangs downwardly from the outer end of the tray, due to the inherent lack of beam strength in ordinary paper used in an office environment for printing by office copiers, printers and facsimile machines.
Particularly in the case of moving bin sorters of the types generally disclosed in U.S. Pat. No. 5,393,047, in which the trays are relatively close together at their outer ends while being opened at their inner ends for feeding sheets between the trays, avoidance of overhang of the sheets from the outer end of the tray above the sheet receiving tray and resultant drooping of the outer ends of such sheets is necessary. This is because the drooping of the outer ends of such sheets interferes with freedom of movement of sheets into the sheet receiving tray below. Therefore, trays have been relatively long, as mentioned above.
Also, in the case of sorters of the moving bin types, as referred to above, the trays have been disposed at a relatively low angle of inclination from horizontal, from the point of infeed of sheets, due to the need to eliminate, as much as possible, the tendency of succeeding sheets fed into a tray to displace proceeding sheets in a sheet feeding direction. This tendency results in faulty alignment of the trailing edges of the sheets against the ususal back stop, and such misalingment is unsatisfactory in the case of sorters which have facilities for automatic in bin or tray stapling.
The cause of the tendency of successive incoming sheets to displace preceding sheets is the speed of contact of the incoming sheets with the previous sheet combined with the interfacial drag friction of the two sheets resulting from moisture in the incoming sheet, static attraction or other factors.